Method of producing cast refractory and similar articles



T. E. FIELD Oct. 7, 1941.

METHOD OF PRODUCING CAST REFRACTORY AND SIMILAR ARTICLES Filed April 29, I939 N wM zzmvfi N WMN Patented Oct. 7, 19 41 METHOD OF PRODUCING CAST REFRAC- TORY AND SIMILAR ARTICLES Theodore E. Field, Louisville, Ky., assignor to Corhart Refractories Company, Louisville, Ky., a corporation ofDeiaware Application April29, 1939, Serial No. 270,810

4 Claims.

This invention relates to an improvement in the method of producing cast refractory and similar articles from molten oxides and the like, and is particularly concerned with the method of molding and cooling such cast articles.

When a relatively large casting is made in a cold mold, the material in solidifying is first chilled on its exterior surfaces in contact with the mold nearly to the temperature of the mold. The molten interior however continues to give heat to this first layer and reheats it to an amount dependent on the available heat and the degree of insulation of the mold. Thus in the case of a large casting in an insulated mold by the tim the inside is solid the outside is relatively hot and the whole casting can be annealed by cooling slowly without introducing excessive strains.

When however a relatively small casting is made in a cold mold, the available heat from the molten interior is limited and when the entire casting has solidified, the outside is still much colder than in the case of a large casting. In cooling such an article greater strains are produced which may cause cracks to develop and ruin the casting. Even if the article does not crack on cooling it may subsequently crack when being heated in service since a state of'strain exists in the casting until relieved by cracking.

In order to diminish the difference in temperature between the outside and inside of'a small casting and thus permit more successful annealing, it is desirable to cast into a preheated mold. Casting into a preheated mold has the further advantage of improving the sharpness of the casting. It would be possible to preheat a mold of suitable material in a muffle furnace but it is awkward to handle the hot molds and for any considerable number of molds, the, preheating equipment would have to be extensiv Several plans have been proposed for preheating the molds but all of such plans as far as I am aware either involve diflicult manipulation, elaborate equipment or lack of flexibility for different size castings.

I have discovered that a satisfactory and advantageous method of preheating a mold of suit able material is to surround it with molten material of high melting point. The volume of the surrounding molten material, which has a definitemelting point, is accurately proportional to the amount of heat in the molten material to be cast. By adjusting the volume of this surrounding material any desired quantity of heat can be made available for the purpose of better annealing the casting. The surrounding molten material may be confined with a suitable container surrounded with insulating powder such as Silocel to further control the cooling cycle.

I prefer to use for the preheatingliquid, material from the same furnace which is to pour the casting itself. In this case the mold will not be preheated to the melting point of the material but this is ordinarily not necessary. If a higher preheating temperature is desired for special cases, molten material from a furnace pouring higher melting point material can be used. Lower temperatures of preheating can be obtained by waiting a shorter time for the mold to heat up before casting. Since the preheating material when cold can be broken up and returned to the furnace, the cost of this treatment represents substantially only the electricity used in melting it and the cost of the exterior mold, while it has th advantage of dispensing with elaborate equipment and of giving an accurately reproducible cooling cycle with unskilled labor. The efiiciency of the heat utilization in my proc-- ess can be further increased by including multiple castings so arranged in a single container mold that each receives th same amount of heating from the surrounding molten material.

As mold for the casting, any material which is a reasonably good thermal conductor and which will not disintegrate at the temperatures obtained by preheating can be used. I prefer however to use graphit because of its ready machinability and inert character. In the short time required for preheating a thin mold, oxidation of graphite is slight and once the molten refractory starts to freeze against it, further action ceases. For the exterior container any material which will retain the molten refractory can be used. I prefer to use sand bonded with linseed oil and baked.

Referring to the accompanying drawing in which Fig. 1 is a longitudinal central section of an assemblage for casting small articles according to my invention and Figure 2 is a cross-sec tion thereof on the line 2-2, A represents a mold, which may be of graphite, for the desired casting. B is the space which will be occupied by the preheating liquid which is enclosed in the exterior container C which may be made of sand slabs. D is the riser through which the preheating molten material is poured. The various volumes B are filled from the one riser D since the molds A are surrounded on four sides by this preheating space. E is the riser through which the castings themselves are filled after the molds 2 A have taken up the desired amount of heat Having thus described my invention, what I claim is:

1. The method of producing cast refractory and similar articles which comprises preheating a thermally conducting mold by partially surrounding it with molten material of high melting point and subsequently pouring the desired casting into the mold so heated and permitting the article to solidify while the mold is surrounded by the said material;

2. The method of producing cast refractory and similar articles which comprises controlling the annealing cycle by the disposition of an appropriate quantity of molten material of high melting point exterior to a mold in which the casting is made and allowing the combined castings to solidify slowly.

3. The method of producing cast refractory and similar articles which comprises making the casting in a mold which has been preheated by partially surrounding it with molten material of high melting point which is further present in an amount suflicient to give a desired annealing cycle and solidifying the combined castings slowly.

4. The method of producing cast refractory and similar articles which comprises pouring molten material around the exterior of a mold and then pouring the desired refractory material into the mold and permitting both pourings to solidify.

THEODORE E. FIELD. 

